Thanks for all the responses. Incidentally, I am neither pro- nor anti-roundabout, but would like to see them built with up-to-date "best practices", hopefully not sacrificing cyclist safety for motorist safety. Also, when negotiating them by whatever means, it helps to know what hazards to look out for.
With that in mind ... Matt Logan commented: "It sounds like one of those studies was on roundabouts with speeds greater than 30mph ... It is unclear from the abstract if that is the speed within the roundabout, or prior to the roundabout. ..." In the non-abstract part of "Safety effects of roundabouts in Flanders: signal type, speed limits and vulnerable road users." Accid Anal Prev. 2007 May;39(3):591-9. Epub 2006 Nov 21. http://tinyurl.com/2qtpx5 the authors go on to write: "Vulnerable road users, who typically travel on smaller roads with lower speed limits, are in some cases more likely to become victims of a road accident after the construction of a roundabout. For example, the number of accidents involving vulnerable road users is up by 28% on 50 km/h×50 km/h intersections (the largest subgroup) when there used to be traffic lights. Although the total number is down by 14%, the risk of getting more seriously injured when involved in an accident has also increased from 3 to 17 fatalities per 100 injury accidents on previously signalized junctions and 12 to 19 on intersections without traffic lights before. ...". Since 50 kph = 31 mph, this is not a very reassuring finding for us cyclists. Matt gave also gave a link I was not aware of : "The WisDOT site ( http://www.dot.wisconsin.gov/safety/motorist/roaddesign/roundabout.htm ) suggests that there is a 10% reduction in bicycle crashes provided by roundabouts. WisDOT seems to have obtained this data from an Insurance Institute for Highway Safety study of 24 roundabout intersections in eight states, and other studies." Ever the skeptic, I tracked this one down via www.iihs.org/research/bibliography.html which lists: Persaud, B.N.; Retting, R.A.; Garder, P.E. and Lord, D. 2001. Safety effect of roundabout conversions in the United States: empirical Bayes observational before-after study. Transportation Research Record 1751:1-8. Washington, DC: Transportation Research Board. I retrieved this paper. The reference for the claimed "10% reduction" apparently is their reference #5, Elvik, R., A. B. Mysen, and T. Vaa. Traffic Safety Handbook (in Norwegian). Institute of Transport Economics, Oslo, Norway, 1997. Persaud et. al. comment about this study, "Bicycle crashes were reduced by 10 to 20 percent. However, the Elvik et al. study was a meta-analysis that included some circular intersections not meeting the typical definition of modern roundabouts. In addition, the extent of the effects of the regression-to-the-mean bias was not known." Since the Elvik study has some problems (e.g. apparently no effort to adjust for regression to the mean, which some other studies take into account) and it contradicts several other more recent studies, I am cautious about the claimed 10% reduction. Unfortunately, this 10% claim gets repeated in literature from other states (e.g. www.azdot.gov/CCPartnerships/Roundabouts/faq.asp ), thus achieving some "veracity by uncited repetition". Matt also mentioned WisDOTs advice for bicycling through roundabouts. Also helpful is a well illustrated presentation "Bicycles at Roundabouts: State of the Practice" TRB National Roundabout Conference May 24, 2004 by Michael M. Moule, PE, PTOE, LCISpecial at: www.teachamerica.com/roundabouts/RA055A_ppt_Moule.pdf Four additional references regarding bicycles and roundabouts with full text on the web are: 1. What roundabout design provides the highest possible safety? Swedish National Road and Transport Research Institute Nordic Road & Transport Research No. 2 · 2000 www.alaskaroundabouts.com/Nordic2safety.pdf "As can be seen in Table 1, at the two-lane roundabouts the total observed numbers of accidents and injuries are more than twice those predicted. For the single-lane roundabouts, on the other hand, there is very good agreement between the observed numbers of accidents and injuries and the predicted numbers... Overall, at single-lane roundabouts there were 18 accidents involving cyclists on the carriageway and 10 accidents with cyclists on a bicycle crossing. At the same time, the total number of cyclists bypassing the roundabouts on a bicycle crossing is about 1.7 times the number travelling through them on the carriageway. If we construct the risk index as "No. of accidents per the sum of the products no. of motor vehicles x no. of cyclists", the risk is about 2.5 times greater for cyclists on the carriageway than for cyclists on a bicycle crossing." 2. Can Modern Roundabouts Safely Accommodate All Users? www.mtjengineering.com/pdfs/Gene_Russel_Paper.pdf "... there is no reliable U.S. data on the effect of roundabouts and bicycle travel. In countries such as Sweden and the Netherlands where bicycle travel is extensive, special provisions for bicycles are common. In the Netherlands, School and Minnen studied bicycle safety and concluded the safest approach was to conduct separate bike paths so that the bicycles crossed the path of vehicles outside of the roundabouts--usually yielding to motor vehicles (Schoon and Minnen, 1994). In the U.S., the primary recommendation is to not have bicycle lanes run through a roundabout, but to terminate them some distance prior to the roundabout. At the termination, a bicycle ramp to an adjacent sidewalk is usually provided. Thus, a bicyclist has the option of riding through the roundabout or diverting to the sidewalk via the ramp and riding or walking his/her bicycle through the roundabout on the sidewalk shared with pedestrians. " 3. Accommodating Vulnerable Road Users in Roundabout Design. http://www.tac-atc.ca/english/pdf/conf2004/Furtado.pdf This covers several specific design features. Indeed, the devil is in the details. 4. Traffic Safety Effects of Roundabouts: A Review with Emphasis on Bicylist's Safety. 18th ICTCT Workshop www.ictct.org/workshops/05-Helsinki/S3_Daniels.pdf This concludes "No final evidence exists about the differences in safety level between different types of cycle facilities. The available research results indicate that roundabouts with separated cycle lanes are safer than roundabouts with mixed traffic or roundabouts with adjacent cycle lanes. The rate of bicycle accidents (number of bicycle accidents per vehicle kilometre) on roundabouts with separated cycle lanes and priority for bicyclists is somewhat higher compared to separated cycle lanes with no priority for bicyclists. A larger central island appears to be safer for bicyclists." Overall, I'll be quite cautious cycling through multilane roundabouts that replace signalized intersections. When the motor vehicle traffic is heavy, I would choose either a separate bicycle path/lane or a bicycle crossing if available. I hope the proposed roundabout offers those options. Jim T
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